1. Field of the Invention
The present invention relates to an image forming apparatus that performs gradation correction, a method of controlling the same, and a storage medium.
2. Description of the Related Art
Conventionally, in an image forming apparatus, an original conveying system of an image reading unit that conveys an original and reads an image of an original being conveyed, and a recording material-conveying system of a printing unit for conveying recording materials are constructed independently of each other.
More specifically, the original conveying system and the recording material-conveying system are each provided, independently of each other, with a sheet feeder from which originals or recording materials are fed, a sheet feeding unit, guiding members for forming predetermined conveying paths, and so on. Further, the original conveying system and the recording material-conveying system are each provided with a plurality of conveying roller pairs, drive force transmission units for transmitting drive forces to the plurality of conveying roller pairs, motors as drive sources, drive circuits of the motors, a sheet discharging section, and so on.
For this reason, it has been inevitable that the entire mechanism construction of the image forming apparatus becomes increasingly complex and the cost and size of the apparatus are increased.
To solve these problems, there has been proposed an image forming apparatus in which an image reading unit is provided in a recording material-conveying path extending from a sheet feeder to a sheet discharger, whereby respective path sections of the original conveying system and the recording material-conveying system are formed as a section which can be shared between the two systems, to thereby attain reduction of the size of the image forming apparatus (see e.g. Japanese Patent Laid-Open Publication No. 2000-185881).
Further, conventionally, there has been known a method in which an image forming apparatus outputs a test chart formed by a specific gradation pattern to a recording material as an image, reads the gradation pattern on the recording material using an image reading unit, and performs gradation correction based on information obtained from the read image. Based on this method, image quality is preserved, improved, or stabilized (see e.g. Japanese Patent Laid-Open Publication No. H07-298072).
In the above-mentioned technical background, the image forming apparatus disclosed in Japanese Patent Laid-Open Publication No. 2000-185881 has the image reading unit arranged in an intermediate portion of the recording material-conveying path e.g. between a fixing device and the sheet discharger, and hence the path for conveying an original to be read becomes long. This configuration makes it difficult to reduce time for reading the original.
Further, since the image reading unit is provided in the recording material-conveying path used for usual printing, when an original is in the recording material-conveying path, it is impossible to perform a printing operation. Therefore, it is required to stop the printing operation during an original reading operation.
Further, the technique disclosed in Japanese Patent Laid-Open Publication No. H07-298072 has a problem that the user is required to set the output test chart on the reading unit by himself/herself. Further, to perform gradation correction with increased accuracy, a plurality of test charts are needed, and hence the user is required to perform a test chart-setting operation each time. Further, if a recording material to be used is a colored paper sheet or a sheet on which printing has been performed, it is impossible to properly perform gradation correction.